1. Field of the Invention
This invention relates to laminated glazings and in particular to bullet resistant glazings.
2. Summary of Related Art
Bullet resistant glazings comprise a laminated structure that includes multiple glass plies and at least one impact resistant ply. These glazings may be installed in vehicles and to facilitate installation the glazing may be provided with a step adjacent its periphery, the step extending around part or all of the periphery. The step results from one or more of the plies extending beyond the remaining plies, and in this specification the ply or plies which thus extend beyond the others will be referred to as the xe2x80x9couter layerxe2x80x9d. The outer layer normally has a greater peripheral dimension than the remaining plies and is usually a single glass ply, which may be annealed, semi-toughened or toughened, but it may also comprise a laminate such as two glass plies bonded by a suitable plastics layer or layers. The xe2x80x9cstepxe2x80x9d of the outer layer enables the glazing to be fitted into the glazing channels of vehicle openings. However, the outer layer must be thick enough in order to possess the structural strength to support the weight of the glazing when fitted into the vehicle opening and to resist dynamic loadings that occur when the vehicle is in motion or the step is likely to be damaged, which may result in the body of the glazing breaking away from the step and falling out of the vehicle opening. Furthermore, the application of a conventional ceramic obscuration band around the periphery of the glazing (which will inevitably cover at least part of the step) weakens the glass covered by the obscuration band thereby reducing the structural strength in the stepped region.
Bullet resistant glazings used in vehicles may have a thickness up to 70 mm or more and a consequence the outer layer may be up to 9 mm thick or more. In some specialist vehicles (e.g. military vehicles) where ballistic protection is required, the thickness of the glazing channels may be set during manufacture of the vehicles at the required thickness to accommodate the bullet resistant glazing. However, there are instances where bullet resistant glazings are installed into mass-produced vehicles and it is not practical to change the tooling used in the manufacture of the vehicle bodywork to alter the width of the glazing channels from conventional thicknesses to greater thicknesses so as to accommodate bullet resistant glazings. As a consequence these vehicles are individually adapted to accommodate the bullet resistant glazings and this may be very expensive.
It would be desirable to provide a bullet resistant glazing suitable for installation in glazing channels of conventional thicknesses.
According to the invention there is provided a laminated bullet resistant glazing comprising a plurality of glass and plastics plies arranged in at least two layers including an outer layer and an inner layer, wherein the outer layer extends beyond the inner layer so as to form a step which extends around at least part of the periphery of the glazing, and wherein the glazing is reinforced with a band at least partially positioned on the step, the band having at least first and second longitudinal faces wherein the first longitudinal face is in contact with the step and the second longitudinal face is in contact with an adjacent portion of the glazing.
The band enhances the support strength of the outer layer of the glazing and enables the manufacture of a bullet resistant glazing with the outer layer being reduced in thickness. Such a glazing may be accommodated in conventional automotive glazing systems of mass produced vehicles which have standard glazing channels which are less than about 6 mm thick.
The band is preferably comprised of a ballistic resistant material which additionally provides ballistic protection around the stepped region of the glazing which traditionally has been ballistically weak, and reduces or prevents spall, which results from breakage of the step, entering the interior of the vehicle.
The band may be comprised of metal or alternatively from a fibre reinforced material. Preferably the fibre is an aramid fibre.
The band may be of angled construction, i.e. comprising two strips which meet at an angle. The strips may be joined at right angles with a longitudinal face of the first strip mounted on the step and a longitudinal face of the second strip mounted on the periphery of the adjacent plies. This arrangement further enhances the support strength of the outer layer.
At least part of the band may be embedded in an interlayer which bonds the outer layer to the inner layer. Such an arrangement further enhances the support strength of the outer layer.
The embedded part of the band may have a thickness in cross-section less than that of the remainder of the band. Such a band may be accommodated between the outer and inner layers of the glazing without having to alter the thickness of the plastic ply or plies (or interlayer) which bonds these layers.
Preferably the face of the band mounted on the step is co-extensive therewith.
An adhesive may bond the band to the glazing and preferably the adhesive is polyurethane.
The thickness of the band may be in the range 2 to 16 mm and is preferably in the range 2 to 4 mm. The combined thickness of the step and the band may be in the range 5 to 30 mm.